Optimus was never cool. Perhaps in "More Then Meets The Eye" he was reasonably cool and in the movie he was way too cool (which is why, when I watch it now, it was painfully obvious he was going to die. I mean he would never look that cool if unless they're trying to get the audience to like him so much that when he died it would be all the more tragic.) Otherwise he was a pathetic leader. Not necessarily the worst, Ultra Magnus led the Autobots to slaughter on the planet of junk, and Rodimus, well we all know about him, and Star Saber was an english prick, and suspected pedophile. But Optimus Prime was neither cool nor was he a compitant leader.
